Steroids

Steroids

Steroids are a family of lipid molecules that includes cholesterol, steroid hormones, and bile salts. These amphipathic molecules (containing both hydrophobic and hydrophilic regions) are derived from two-carbon acetyl-CoA units, whose combination leads to the formation of isoprenoids (five-carbon isoprene molecular units), and finally to the formation of a seventeen-carbon tetracyclic hydrocarbon, the steroid skeleton. Figure 1 shows the basic steroid skeleton structure, made up of three six-membered rings and one five-membered ring. The fused six-membered cyclohexane rings each have the chair conformation . Each member of the steroid family has a structure that differs from this basic skeleton in the degrees of unsaturation within the ring system and the identities of the hydrocarbon side chain substituents attached to the rings. These substituents are in most cases oxidized to alcohol, aldehyde , ketone , or carboxylic acid functional groups .

The general term sterol refers to a subgroup of steroids that contain an alcohol functional group, which is signified by the -ol ending. Steroids are found predominantly in eukaryotic cells , with cholesterol being the most abundant steroid molecule. It contains twenty-seven carbons, has an alcohol functional group at C-3, a methyl group at C-13, and a branched aliphatic hydrocarbon (eight carbons) unit at the C-17 carbon atom. It is the basic building block for all the other steroid molecules. The biosynthesis of other steroids from cholesterol yields molecules that have fewer carbons, are more polar and more oxidized, and have smaller and more oxidized hydrocarbon units at C-17. It should be emphasized that cholesterol and most steroids contain predominantly single (C–C) bonds and take on non-planar structures. Intracellular cholesterol is predominately found as part of (embedded in) the plasma cell membranes. Because of cholesterol's bulky structure, it does not embed well into the lipid bilayer structure of a membrane and as a result disrupts the order or regularity of the membrane. Increasing levels of embedded cholesterol, which can be as high as 25 percent of membrane volume, correlates with increasing the fluidity (as opposed to rigidity) of the membrane.

The level of extracellular cholesterol in blood serum correlates with the degree of advancement of atherosclerosis and the development of coronary heart disease. The serum cholesterol is obtained from diet and from biosynthesis, which occurs primarily in the liver of mammals. The usual metabolic pathway for cholesterol biosynthesis involves a sequence of more than twenty reactions, each catalyzed by a specific enzyme. The committed and the rate-limiting step in the sequence is the synthesis of a six-carbon molecule, mevalonate, catalyzed by the enzyme 3-hydroxy-3-methylglutaryl CoA reductase (HMG CoA reductase). The development of drugs that inhibit the activity of HMG CoA reductase (and that reduce levels of serum cholesterol), has led to a decline in coronary heart disease. These drugs have structures similar to that of mevalonate and serve as competitive inhibitors of HMG CoA reductase. The binding of a competitive inhibitor to the enzyme and of the substrate mevalonate to the same enzyme are mutually exclusive events. One of the most potent inhibitors of HMG CoA reductase is the drug lovastatin, which binds very strongly at the active site of the enzyme, and, as a result, serum cholesterol levels in humans are decreased by as much as 20 percent.

The hydrophobic, water-insoluble cholesterol is transported in blood to cells predominantly as part of high density and low density lipoprotein particles (HDLs and LDLs, respectively). LDLs transport cholesterol to extrahepatic tissues. The LDL particles bind to LDL receptors on the cell membranes, facilitating cholesterol deposition at the cells, for use primarily as a component of the membrane. HDLs carry out a similar transport function but also return cholesterol to the liver, where it can be metabolized. In this way HDLs decrease the levels of the cholesterol that contributes to the deposition of plaque in arteries and is implicated in heart disease. In a number of cases, patients have been found to have defective genes that code for the LDL receptors. In these cases the LDL particles cannot deposit the cholesterol at cell sites. The LDLs remain in the blood, and eventually their lipid molecules accumulate on the arterial walls, which can lead to blockage of arteries and a heart attack.

Cholesterol is the precursor of other important steroid metabolites , which include bile salts and steroid hormones. Bile salts, which are the major breakdown product of cholesterol, resemble detergents, which are amphipathic molecules (having both polar and nonpolar regions). Their primary function is to emulsify dietary lipids. This interaction between bile salt and lipid increases the surface area of exposed lipid, which greatly enhances the ability of lipase enzymes to get access to and hydrolyze lipid molecules, thereby promoting their absorption and digestion. Bile salts are synthesized and secreted by the liver, stored in the gall bladder, and pass through the bile duct and into the small intestine. Bile salts are the major metabolic product of cholesterol, their manufacture accounting for the consumption of approximately 800 mg/day of cholesterol in a normal human adult. (On the other hand, less than one-tenth that amount of cholesterol is utilized for steroid hormone synthesis.) A major bile salt is glycocholate.

Cholesterol is also the precursor of all the steroid hormones, which can be subdivided into five major classes. The first and second classes of hormones, the mineralocorticoids and the glucocorticoids , are synthesized in the adrenal cortex. The mineralocorticoids (e.g., aldosterone) regulate the body's ion balance by promoting the reabsorption of inorganic ions, such as Na+, Cl−, and HCO3−, in the kidney. As a result, they are involved in the regulation of blood pressure. The glucocorticoids (e.g., cortisol) regulate gluconeogenesis and, in pharmacological doses, inhibit the inflammatory response. The third class includes progesterone , associated with the female reproductive cycle and synthesized in the cells of the corpus luteum; it prepares the lining of the uterus for implantation of the ovum and is essential for the maintenance of pregnancy. The sex hormones are synthesized in the male and female gonads and in the placenta. These hormones, the fourth and fifth classes, are androgens (primarily testosterone) and the estrogens (primarily estradiol). These two classes of hormones are associated with the development of the secondary sexual characteristics of males and females, respectively. They exert powerful physiological effects in humans because of their importance in the regulation of a variety of vital metabolic processes.

Steroid hormones, like all hormones, are chemical messengers. They are synthesized in the cells of an endocrine gland, secreted by the cells into the bloodstream, and travel to target organs in which they direct cell-to-cell communication and the "global regulation" of metabolism in a multicellular organism such as humans. The levels of the steroid hormones are also highly regulated, with levels in the blood or in cells being very small, typically less than micromolar amounts. Because of their hydrophobic

character, they must associate with carrier molecules for their transport in the blood.

In contrast to polypeptide hormones that bind to hormone receptor proteins embedded in the plasma membranes of cells, the hydrophobic steroid hormones pass from the bloodstream into cells readily via passive diffusion across the membrane. Although the steroid hormones can in principle enter all cells, the only cells that are responsive to steroid hormones are those cells that contain proteins called steroid hormone receptors. These receptors reside in an inactive state either in the cytoplasm or in the cell nucleus. There are specific hormone receptors for each of the hormone types: estrogen , androgen, progesterone, glucocorticoid, and mineralcorticoid. As a result of the hormone binding to the recognition site of its hormone receptor, an inactive receptor is transformed into a functionally active one. These active hormone-receptor complexes are ligand -activated transcription factors, which are then able to migrate to the DNA in the nucleus and bind to the promoter regions of a specific subset of genes. This stimulates the transcription of genes that are sensitive to the presence of the hormone. These genes are only expressed or transcribed when the hormone is present. The messenger RNA that is produced is then translated into a new set of proteins. As a result of this stimulation of gene expression, the metabolic character of the cell is dramatically changed.

Anabolic steroids are synthetic substances related to male sex hormones (androgens). Although it is illegal in the United States to possess or distribute anabolic steroids for nonmedical use, a "black market" for them exists, and many amateur and professional athletes take them to enhance performance. In many cases, the athletes take doses that are extremely high—perhaps 100 times the doses that might be prescribed for medical use. As a result, they put themselves in real danger of short-term and long-term health problems. Blood testing, as has been used in the Olympic Games, can detect, identify, and quantify the presence of anabolic steroids in the blood of athletes, which can lead to the disqualification of an athlete.

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steroids

steroids comprise a large group of substances that mediate a very varied set of biological responses. The most widespread in the body is cholesterol, an essential component of cell membranes, and the starting point for the synthesis of other steroids — the sex hormones, adrenal cortical hormones, and the bile salts.

The steroids are grouped together because their chemical structures are all very similar. The steroid chemical nucleus consists of four carbon rings, three 6-sided and one 5-sided, joined together by their edges. The specificity of their different biological actions is due to the various groups attached to a common nucleus. When alcohol groups (OH) are attached, steroids should properly be called sterols (such as cortisol), whereas ketone groups (C=O) make them sterones (such as aldosterone).

Different steroids react with different membrane receptors in cells, and a precise fit between the steroid and the receptor is required. Therefore a single steroid can be expected to have a specific effect.

Steroids have major responsibilities as hormones, controlling metabolism, salt balance, and the development and function of the sexual organs as well as other bodily differences between the sexes. Steroids in the form of bile salts assist in digestive processes, while another steroid is a vitamin that takes part in calcium control.

Steroid hormones

Steroid hormones are made and secreted into the circulating blood by the cortex of the adrenal glands and the gonads (testes or ovaries). Mostly, their secretion is regulated by hormones from the pituitary gland, and those in turn by chemical messages from the hypothalamus.

Two types of steroids are released from the adrenal cortex, the glucocorticoids, mainly cortisol (hydrocortisone) and the mineralocorticoids, mainly aldosterone. Both types of hormone are important in stress situations such as disease or injury.

Glucocorticoids mobilize glucose, which is particularly important in fasting conditions. They do so by promoting glucose formation from non carbohydrate sources in the liver, increasing glycogen levels, and raising the blood glucose concentration. Liberation of glucocorticoids from the adrenal cortex is caused by adrenocorticotrophic hormone (ACTH), released from the pituitary gland. When the glucocorticoid level in the blood is low, ACTH is released, but when it is high the release of ACTH is suppressed. This is a good example, one of many that occur in the body, of a feedback system. Large doses of glucocorticoids are anti-inflammatory and at one time it was thought they would provide suitable treatment for inflammatory conditions such as rheumatoid arthritis. However, the excessive breakdown of proteins, mobilized to form glucose in the liver, leads to muscle weakness and osteoporosis and there is also ‘moon face’ and obesity. This describes exactly the features of Cushing's syndrome, a condition caused by excess secretion of corticosteroids. Furthermore, if therapy with glucocorticoids is withdrawn rapidly the pituitary system is so suppressed that the body's own system takes a while to trip in, leading to an ‘Addisonian crisis’, mimicking Addison's disease in which there is a deficiency in glucocorticoid production. With due precautions, however, corticosteroids remain a useful treatment in some severe allergic and inflammatory conditions.

The mineralocorticoid aldosterone is released at an increased rate from the adrenal glands if the body is salt depleted; this is stimulated by a complex detecting system in the kidneys, resulting in an increase in circulating angiotensin, which acts in turn on the adrenal glands. Aldosterone promotes sodium reabsorption by the kidneys, so that there is less salt in the urine, thus correcting the deficiency. It acts on sweat glands similarly, diminishing salt loss in sweat.

Male steroid sex hormones, androgens, are produced in the testes. Testosterone is the most important of the androgens and is responsible for controlling the production and maturation of sperm, as well as male characteristics, such as the distribution of body hair. Anabolic steroids are derivatives of testosterone and act on androgenic receptors. They build up muscle mass and cause virilization — features of masculinity. They are useful in the treatment of debilitated patients to help restore their physique. Unfortunately these substances have been taken illicitly by athletes for body-building. Their use carries considerable risk, as sudden withdrawal will leave the body's natural processes suppressed, by interference with the feedback system as described above. Detection of the use of anabolic steroids has become difficult as it appears that one that is commonly used, namely nandrolone, can be synthesized by the body itself in small quantities, especially when under physical stress. Female steroid sex hormones are of two types, oestrogens and progestins, both from the ovaries. Again under pituitary hormone regulation, their relative secretion varies within the menstrual cycle. Oestrogens promote the growth of the lining of the uterus in preparation for implantation of a fertilized egg. Once the egg has been shed from the ovary, the corpus luteum (yellow body), which develops in the cavity left behind, secretes progesterone; this promotes further development of the uterine lining and, if implantation of an embryo occurs, maintains changes here and elsewhere for the duration of pregnancy.

The understanding of these processes is the basis of the contraceptive pill. Synthetic steroids were devised for this purpose, as natural steroids are metabolized by the liver if taken by mouth. As with the other steroid hormones, there are feedback systems involving the pituitary gland. Taking oestrogens inhibits the release from the pituitary of the follicular stimulating hormone that would normally cause maturation of eggs in the ovary: so, no ovulation, no conception. Contraceptive pills usually contain both oestrogens and progestins, which are taken concurrently or sequentially during the 4 week course, menstruation following when the course ceases. A large dose of both an oestrogen and progestin promotes uterine bleeding within a few hours and is the basis of the ‘morning after’ pill.

Steroids and bile

Cholesterol, taken up from the blood into the liver or synthesized there, can be oxidized in the liver to cholic acid. Conjugation of this with taurine or glycine gives the bile salts, taurocholate and glycocholate. These bile salts pass into the small intestine and have important actions in aiding the digestion and absorption of fats. Cholesterol itself is excreted in the bile.

The steroid vitamin

Exposure to ultraviolet light converts a steroid, dehydrocholesterol, in the skin to vitamin D. This is what happens when you sunbathe, but in climes where exposure to the sun is limited it is necessary to supplement the diet with the vitamin. Fish oils are rich in vitamin D and the Eskimo diet ensures that they get a sufficient supply. The vitamin primarily promotes calcium absorption from the gut. Calcium is essential for bone growth and maintenance, muscle contraction, and many signalling processes in the body.

While steroids have many different actions on the body, their mechanism of action is similar in all instances. The receptors for steroids are inside cells (unlike those for many other substances, which are on the cell membrane). The complex formed by combination of the steroid with its specific receptor enters the nucleus and switches on or off the appropriate genes, which then gives rise to the characteristic effect. Their actions are not therefore immediate as with, for example, neurotransmitters, nor are they as rapid as those of the peptide hormones; several hours elapse before the effect appears. To give one example, the receptors for aldosterone are located in the end part of the kidney tubules. Here genes are switched on which lead to the synthesis of the molecules that actually handle the reabsorption of sodium ions from the urine back into the blood. The process becomes more efficient because there are a larger number of molecular entities dedicated to the task.

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Steroids

Steroids

The generic term steroids refers to a group of substances sharing a common basic chemical structure, many of which function as hormones in the human body. The two best-known classes of human steroid hormones are corticosteroids and anabolic-androgenic steroids. Corticosteroids are hormones secreted by the adrenal gland, such as cortisol, which modulate a range of physiologic functions, such as inflammatory responses and blood pressure. Many synthetic corticosteroids have been developed, such as hydrocortisone, beclomethasone, and dexamethasone; these synthetic substances have effects similar to those of naturally occurring corticosteroids and are widely prescribed in medicine for a range of conditions. For example, hydrocortisone is often a component of skin creams used to treat poison ivy reactions or other inflammatory skin conditions; beclomethasone is a common component of inhalers used in the treatment of asthma; and high doses of corticosteroids are administered to recipients of organ transplants to prevent rejection of the foreign tissue. In low dosages, corticosteroids have few psychiatric effects, but higher doses may sometimes cause manic symptoms (e.g., euphoria, hyperactivity, increased self-confidence, and impaired judgment) or even psychotic symptoms (e.g., delusions or hallucinations) in some predisposed individuals. Corticosteroids have very little potential for abuse and are rarely ingested by illicit substance abusers.

Anabolic-androgenic steroids represent an entirely different class of hormones. The prototype hormone of this class is the male hormone testosterone, which is secreted primarily by the testes in males. Anabolic-androgenic steroids produce masculinizing (androgenic) effects—such as beard growth, male pattern baldness, and male sexual characteristics—together with muscle-building (anabolic) effects. These latter effects account for the greater muscle mass and lower body fat of men as compared to women. Many synthetic anabolic-androgenic steroids have been developed over the last fifty years. Like testosterone, these synthetic substances produce both anabolic and androgenic effects; there are no purely anabolic or purely androgenic compounds. In medical practice, the principal use of testosterone is in the treatment of hypogonadal men—men who do not secrete sufficient testosterone in their own bodies, and who therefore require testosterone supplementation to maintain normal masculine characteristics. Aside from this application, anabolic-androgenic steroids have only very limited medical uses, such as in the treatment of certain forms of anemia.

Unlike corticosteroids, anabolic-androgenic steroids are widely abused by individuals wishing to gain muscle and lose body fat. The great majority of these illicit users are male; women generally do not abuse anabolic-androgenic steroids because of the drugs’ undesirable masculinizing characteristics, such as beard growth, deepening of the voice, and shrinkage of the breasts. Men generally do not have to worry about these masculinizing effects and therefore may take doses far in excess of the amounts naturally present in the body. Specifically, an average man secretes between 50 and 75 milligrams of testosterone per week in his testes, whereas illicit anabolic-androgenic steroid abusers often ingest the equivalent of 500 to 1,000 milligrams of testosterone per week. When taken in these very high doses, anabolic-androgenic steroids can produce dramatic increases in muscle mass and strength, making it possible for users to far exceed the upper limits of muscularity attainable under natural conditions, without these drugs. Because of these properties, anabolic-androgenic steroids are widely used by athletes in sports requiring strength or muscle mass for feats such as hitting home runs in baseball or playing line positions in American football. In the United States there have been many recent well-publicized cases of prominent professional athletes who were found to be taking anabolic-androgenic steroids, and this issue became a subject of several congressional hearings in 2005. In addition, anabolic-androgenic steroids are increasingly abused by boys and young men who have no particular athletic aspirations, but who simply want to look more muscular. This pattern of abuse is particularly prevalent in North America, Australia, and some European countries—cultures where muscularity is sometimes portrayed as a measure of masculinity. By contrast, anabolic-androgenic steroids are rarely abused for purposes of body image in Asia, probably because Asian cultural traditions do not emphasize muscularity as an index of masculinity. However, anabolic-androgenic steroids are certainly used by some Asian athletes, especially at the elite level because these individuals are seeking a performance advantage, rather than a bodyimage effect.

In Europe and North America illicit anabolic-androgenic steroid use represents a significant and probably growing public health problem. Taken in massive doses, these hormones may pose long-term medical risks, especially because of their adverse effects on cholesterol levels, which may greatly increase the risk of heart attacks or strokes at an early age (sometimes in the forties or fifties). In addition, high doses of anabolic-androgenic steroids may have psychiatric effects such as irritability, aggressiveness, and even violent behavior (sometimes popularly called “roid rage”) in some individuals. Thus, these drugs may pose a danger not only to users themselves, but even to some nonusers—particularly women—who may become victims of such violence. Men who use anabolic-androgenic steroids for long periods may also suffer depressive symptoms, sometimes accompanied by suicidal thoughts or even successful suicide, if they abruptly stop these drugs. Despite these risks, however, it appears unlikely that illicit anabolic-androgenic steroid use will decline in the near future because these drugs are readily available on the black market and offer a great temptation to men seeking muscle and strength gains.

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Steroids

Medical Discoveries
COPYRIGHT 1997 Thomson Gale

Steroids

People usually think of steroids as drugs that athletes take to build their bodies more quickly. Steroids are more than that. They form an organic compound group that include sterols, D vitamins, bile acids, some hormones, saponins, glucosides (organic compounds that produce sugar) of digitalis, and some carcinogenic (cancer-causing) substances. These compounds may come from a number of different substances and have a variety of functions.

Cholesterol

Sterols, for example, are related to fats and are found in either plants or animals. An common example of a sterol is cholesterol. Cholesterol is found in almost all body tissues, particularly the nervous system, liver, kidneys
and skin. It forms part of cell membranes and is synthesized in the liver and other organs. The body uses cholesterol to produce other steroids. For several decades, doctors have associated cholesterol with the build-up of damaging plaque in the arteries.

Other Steroid Group Members

Saponins are found in the roots of some plants. They can be very dangerous since they can destroy red blood cells. The steroid digitalis is a plant product used to stimulate the heart. It is a dangerous drug that must be administered with care because an overdose can be fatal. Sex hormones that control sexual maturity and reproduction are also steroids. Sex hormones include androgens for male functions and estrogens and progesterone for female functions.

[See alsoSex hormones ; Vitamin ]

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steroids

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

steroids, class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals. In humans, steroids are secreted by the ovaries and testes, the adrenal cortex (see adrenal gland), and the placenta.

The range of steroids is diverse, including several forms of vitamin D, digitalis, sterols (e.g., cholesterol), and the bile acids. Many steroids are biologically active hormones that control a number of the body's metabolic processes. This group includes the male sex hormone testosterone and the female sex hormones estrogen and progesterone. The steroid hormones of the adrenal cortex include glucocorticoids such as cortisone and cortisol (see also corticosteroid drug) and mineralocorticoids such as aldosterone.

Natural or synthetic steroids are used in oral contraceptives and in the treatment of arthritis, Addison's disease, and certain skin ailments. Side effects, related to dosage and length of treatment, can be serious and include high blood pressure, edema, unwanted hair growth, and menstrual cycle disruption. Anabolic steroids, male hormones given to build up strength in seriously ill patients, have been abused by bodybuilders and athletes in an attempt to increase muscle mass and strength.

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steroid

ste·roid
/ ˈsterˌoid; ˈsti(ə)r-/
•
n. Biochem.
any of a large class of organic compounds with a characteristic molecular structure containing four rings of carbon atoms (three six-membered and one five). They include many hormones, alkaloids, and vitamins. ∎ short for anabolic steroid.
PHRASES:on steroids used to suggest a highly exaggerated, enhanced, or accelerated version of something: high-protein gelatin squares, available in bright red or bright green, sort of like Jell-O on steroids.DERIVATIVES:ste·roi·dal
/ steˈroidl; sti-/ adj.

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steroid

steroid Class of organic compounds with a basic molecular structure of 17 carbon atoms arranged in four rings. Steroids are widely distributed in animals and plants, the most abundant being the sterols, such as cholesterol. Another important group are the steroid hormones, including the corticosteroids, secreted by the adrenal cortex, and the sex hormones (oestrogen, progesterone, and testosterone). Synthetic steroids are widely used in medicine. Athletes sometimes abuse steroids to increase their muscle mass, strength, and stamina, but there are harmful side effects. Taking steroids is illegal in sports.

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steroid

steroid Any of a group of lipids derived from a saturated compound called cyclopentanoperhydrophenanthrene, which has a nucleus of four rings (see formulae). Some of the most important steroid derivatives are the steroid alcohols, or sterols. Other steroids include the bile acids, which aid digestion of fats in the intestine; the sex hormones (androgens and oestrogens); and the corticosteroid hormones, produced by the adrenal cortex. Vitamin D is also based on the steroid structure.

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steroids

steroids Chemically, compounds that contain the cyclopenteno‐phenanthrene ring system. All the biologically important steroids are derived metabolically from cholesterol; they include the sex hormones (androgens, oestrogens, and progesterone) and the hormones of the adrenal cortex. See also phytosterols; sitosterol.

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steroid

steroid (steer-oid) n. one of a group of organic compounds that include the male and female sex hormones (androgens and oestrogens), the hormones of the adrenal cortex (see corticosteroid), progesterone, bile salts, and sterols. Synthetic steroids have been produced for therapeutic purposes.

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steroid

steroid One of a group of derivatives of the fused, reduced, ring compound per-hydrocyclopentanophenanthrene. As a group, steroids have a wide range of physiological functions: they include bile acids, adrenocorticoid and sex hormones, and sterols such as cholesterol.

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steroid

steroid One of a group of derivatives of the fused, reduced, ring compound perhydrocyclo-pentanophenanthrene. As a group, steroids have a wide range of physiological functions in animals. Compare PHYTOSTEROL.

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